This invention relates to an intramedullary nail structure and to a method for positioning the intramedullary nail in a bone structure.
A severe fracture in a long bone of the arm or leg such as the tibia or femur bone has a tendency to cause the bone segments created by the fracture to compress, thereby, shortening the length of the bone or mispositioning the bone due to torsion. Presently, a cannulated intramedullary nail that is inserted into an opening made in one end of the bone and passed through the medullary canal past the points of fracture is used to avert such compression or torsion. A guide wire is first inserted in the opening usually made in the proximal end of the bone, and into the distal bone fragment significantly past the fracture sites. The guide wire guides the cannulated nail past the fracture sites. Although the intramedullary nail substantially occupies the medullary canal, it is only capable of retaining length and preventing excessive bone shortening if the bone segments are appropriately fastened, or locked, to the nail.
The major problem in using a locked intramedullary nail is locating distal aperture(s) in the nail and successfully aligning fasteners, inserted through the bone wall, with the apertures. The use of a jig has been proposed that is accurately retained in relationship to the nail by a portion extending into the bone through the proximal opening in the bone and which has an external portion that extends parallel the bone. Alignment means are provided for aligning the fasteners with the apertures in the nail along the external portion. While such a technique is successful at accurately locating the proximal locking fastener(s), the long distance to the distal fasteners from the proximal end of the bone allows relative movement between the jig and the nail which distorts the alignment means. Accordingly, alignment with the distal aperture(s) is not assured and damage to the bone wall or to the nail aperture may result.
A more accurate technique for locating distal apertures is an X-ray imaging technique that utilizes a target device. The target device is positioned at the approximate location of the distal nail aperture and iteratively repositioned until a perfect circular image of the nail aperture is produced. This occurs when the target device is located on the center line of the aperture. Means are provided, relative to the target device, to then locate the insertion point for the fasteners. The problem with such a distal aperture location technique is the cumulative exposure of the patient and the operating team to X-ray radiation which can be excessive if the procedure to properly position the target device requires excessive time. It is also less than precise due to optical deformation and wrong perspective of the image.
It has been proposed in U.S. Pat. Nos. 4,705,027 and 4,817,591 to provide an intramedullary nail having a distal tip with a slot which engages a screw previously inserted through a distal portion of a bone. Such an intramedullary nail also is disclosed in U.S. Pat. No. 4,846,162. Other intramedullary devices such as nails are disclosed in U.S. Pat. Nos. 2,381,050; 3,216,414; 4,498,468; 4,827,917; 4,805,607; 4,913,137 and 51057,103.
While nails having a fixed slot which engages a previously introduced screw or stud into a distal end of a bone have been proposed, they are difficult to use. The slot utilized is small. That is, it has a cross-section dimension less than the horizontal cross-sectional area of the nail. Therefore, it is difficult to align properly with a small screw or stud previously positioned in the bone transverse to the nail. Such difficulties also arise because the nail may become rotated about its vertical axis during insertion through the medullar canal. In addition, the nail surrounds only a portion of the circumference of the screw or stud so that it is free to move relative to the screw or stud.
Accordingly, it would be desirable to provide an intramedullary nail which can be properly positioned quickly to minimize patient exposure to radiation. In addition, it would be desirable to provide such a nail which can be positioned to surround one or more mating fasteners and which can be subsequently removed easily.